Casimir IV (Polish: Kazimierz IV or Kaźko Słupski,[1] German: Kasimir IV[2] or Kasimir V [3] ) (1351 – January 2, 1377) was a duke of Pomerania in Pomerania-Stolp since 1374.
Casimir was the son of Bogislaw V, Duke of Pomerania and Elizabeth of Poland. His maternal grandfather Casimir III the Great, last King of Poland from the Piast dynasty, brought him up at his court as his favorite - the king had no legal male successors. After grandfather's death in 1370, young Casimir initially became his partial successor, as the last will gave him lands of Dobrzyń, Bydgoszcz, Kruszwica, Złotów and Wałcz. Yet, his ambitions were soon thwarted by Louis I of Hungary, who became the next king of Poland on the ground of earlier pacts, and nullified the Piast's last will. Duke Casimir only held the land of Dobrzyń as a temporary fief.[4]
In 1360, Casimir married his first wife Kenna of Lithuania. She was a daughter of Algirdas and Uliana Alexandrovna of Tver, raised in the Eastern Orthodox faith. With her marriage, she joined the Roman Catholic Church and was baptised again under the name "Johanna". She died on 27 April 1368, leaving no children.
After a year, Casimir IV married his second wife Margaret of Masovia. She was a daughter of Siemowit III of Masovia and his first wife Euphemia of Opava. They had no children, too. After the death of Casimir, she married Henry VIII, Duke of Lubin and Brzeg.